This invention relates to an airborne glide slope tracking system and more particularly to an airborne glide slope tracking system for automatically or semiautomatically landing an aircraft.
The need for a highly reliable and safe landing system for aircraft has been recognized. It has also been recognized that such system should be fully operable under adverse weather conditions with reliability. Such systems should automatically land an aircraft safety in fog or rain at night, with heavy pay loads and provide smooth landings under any such conditions. In order to meet the requirements of reliability and to provide for smooth landings under adverse conditions, an automatic landing system must contain control equipment which is insensitive to outside disturbances normally encountered in landings.
An early system for an integrated glide path/flare automatic flight control is disclosed in the U.S. Patent of Doniger U.S. Pat. No. 3,892,373. As disclosed in the Doniger patent, a system controls an aircraft during integrated glide path capture and tracking and flare maneuvers when automatically landing the aircraft. That system eliminated the need for explicit switching to initiate the flare maneuver and the flare control channel is effectively exercised during the glide path capture and tracking maneuvers to eliminate extensive pre-land testing that would otherwise be required if the flare control channel were switched on at lower critical altitudes.
A more recent development in a flare control system for the automatic landing of an aircraft is disclosed in my copending application entitled xe2x80x9cAirborne Safe Landing Power Control System and Method,xe2x80x9d Ser. No. 09/467,072 which was filed on Dec. 20, 1999. That system includes a computer and a minimum air speed program as a function of altitude. A radio altimeter or the like senses the instantaneous altitude of the aircraft while a pitot tube or the like measures indicated air speed. A computer program compares air speed with actual air speed for a given altitude. A server motor is provide for decreasing engine thrust when the actual air speed exceeds the programmed air speed at any given altitude. In addition, an inhibitor inhibits the decrease in engine thrust if the air speed drops below the programmed air speed.
The present invention which also embodies a computer and program can be programmed into the same computer as my aforementioned airborne safe landing power control system to provide a fully automated landing system, or may be embodied in a semiautomated landing system wherein the pilot exercises minor control adjustments during the glide slope maneuver.
It is presently believed that a glide slope tracking system in accordance with the present invention will more closely maintain a referenced speed and sink rate then prior art devices. Such systems should also reduce glide slope errors and automatically or semiautomatically correct for any such errors. Such systems will more tightly control glide slope tracking throughout the glide slope maneuver from capture to flare. In addition, the glide slope tracking system disclosed herein controls the flight path by changes in power with automatic or semiautomatic change in pitch in response to any change in power.
In essence, the present invention contemplates a glide slope tracking system for maintaining an aircraft on a preselected glide slope at a preselected speed during a landing approach. The system includes a computer, computer program, means such as a radio altimeter and means for generating a signal indicative of glide slope error. The system also includes means such as a throttle servo for adjusting the power of an aircraft in response to glide slope error. In addition, means for generating a signal indicative of a difference between the aircraft""s reference angle of attack and the aircraft""s actual angle of attack or air speed error as well as an accelerometer are also provided. The accelerometer is responsive to changes in power and generates a signal which is combined with the signal indicating the difference between the aircraft""s reference angle of attack and its actual angle of attack to produce an output signal. This output signal produces a flight direction pitch command to provide a pitch angle which will be sustained by the power of the aircraft.
The preferred embodiment of the invention also includes a filter or LaPlac transform function to provide a signal which is indicative of how fast the glide slope is changing. This signal is added to the signal which is indicative of glide slope error and height to drive a throttle servo.
The invention will now be described in connection with the accompanying drawings.